Method and system for managing mass registration scenario in two-way radio system

ABSTRACT

A method and apparatus are described for managing a mass registration scenario in a two-way radio system. A site controller in a trunked radio system detects a mass registration condition in which registration requests by subscriber units are likely to collide on an inbound control channel. During the mass registration condition, the site controller initiates a restriction period by instructing subscriber units that are members of particular talkgroups to temporarily cease registration requests. Those talkgroup members are permitted to resume their registration requests when a predetermined delay time has passed since the members were instructed to cease registration, or when a particular silence time has passed without registration activity over the control channel.

BACKGROUND OF THE INVENTION

Trunked radio systems are one solution for permitting two-way radiocommunications, such as voice and data communications, not only betweenindividual users equipped with subscriber radio units, but also amongall active members of particular talkgroups. Conventional two-way radiosystems permit group communications among radio users who tune in to aparticular communications channel, such as a particular frequency, thathas been assigned in advance. Trunked radio systems, on the other hand,do not require members of a talkgroup to select any particularcommunications channel in advance. Instead, communications channels areassigned only as they are needed. The assignment of communicationschannels is performed by a site controller. Users of subscriber unitsremain in wireless communication with a site controller over a duplexcontrol channel, which is comprised of an inbound channel forcommunications to the site controller and an outbound channel forcommunications from the site controller to the subscriber units.

When a communications channel is needed for talkgroup or individualcommunications, a request is made to the site controller over theinbound control channel. Over the outbound control channel, the sitecontroller alerts the relevant subscriber units to the communicationschannel to be used.

Subscriber units can be turned on or off, or they can enter and leave anarea served by a particular site controller, and site controllersthemselves can be in and out of service at various times. To keep trackof which subscriber units are being served by which site controller,subscriber units engage in a registration process in which subscriberunits send registration requests to a site controller and identify thetalkgroup or groups with which they are affiliated. In turn, the sitecontroller registers the presence of the subscriber units and confirmsthe registration by sending registration grants to the respectivesubscriber units. A site controller may also be affiliated with one ormore relays that allow subscriber units to communicate with one anotherdespite being served by different site controllers. Such communicationsmay take place through the intermediary of a backend network.

Trunked radio systems have several advantages over conventional radiosystems, such as a more efficient allocation of the radio spectrum andgreater flexibility in the assignment of subscriber units to multipledifferent talkgroups. However, the use of a trunked radio system posesother challenges. For example, it is possible for the control channel,which can be shared by numerous subscriber units, to be overloaded byradio traffic. Such a situation can arise when several subscriber unitsare attempting to send registration requests at the same time. When twosubscriber units attempt to send messages, such as registrationrequests, on the same channel at the same time, it is often the casethat neither message is intelligible. The two subscriber units whoserequests have collided then need to make a new attempt to send theirmessages. It is known in the art for the subscriber units whose messageshave collided to employ a random back-off routine and to make a newattempt to send the message after a random delay period has passed.Since both subscriber units are not likely to select the same randomdelay period, the messages are not likely to collide in the secondattempt.

The use of a random back-off routine works well during ordinary radiotraffic conditions. However, on occasion, a situation can arise in whichthe amount of subscriber unit registration traffic is too high to besatisfactorily handled by only a random back-off routine. One suchsituation is a mass registration event, where some occurrence leads to alarge number of registration requests to be sent at substantially thesame time. For example, a situation may arise in which one sitecontroller fails, leading many of the subscriber units that wereformerly registered with that site controller to inundate neighboringsite controllers with new registration requests.

Accordingly, there is a need for an improved method and system formanaging a mass registration scenario in a two-way radio system.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separateviews, together with the detailed description below, are incorporated inand form part of the specification, and serve to further illustrateembodiments of concepts that include the claimed invention, and explainvarious principles and advantages of those embodiments.

FIG. 1 is a schematic block diagram illustrating an architecture of atrunked radio system in accordance with some embodiments.

FIG. 2 is a schematic message flow diagram illustrating exemplarycommunications between a site controller and talkgroup members in someembodiments.

FIG. 3 is a flowchart illustrating an operation of a site controller insome embodiments.

FIG. 4 is a schematic message flow diagram illustrating exemplarycommunications between a site controller and talkgroup members in someembodiments.

FIG. 5 is a flowchart illustrating an operation of a site controller insome embodiments.

FIG. 6 is a flowchart illustrating an operation of a subscriber unit insome embodiments.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

The apparatus and method components have been represented whereappropriate by conventional symbols in the drawings, showing only thosespecific details that are pertinent to understanding the embodiments ofthe present invention so as not to obscure the disclosure with detailsthat will be readily apparent to those of ordinary skill in the arthaving the benefit of the description herein.

DETAILED DESCRIPTION OF THE INVENTION

According to an embodiment described herein, a site controller detectsthat an inbound control channel is in a mass registration condition.During the mass registration condition, the site controller receives aplurality of registration requests over the inbound control channel.Among the requests are at least a first registration request from amember of a first talkgroup. In response to the first registrationrequest, the site controller initiates a restriction period by sending arestriction message on an outbound control channel. The restrictionmessage instructs members of the first talkgroup to cease registrationrequests. When the restriction period ends, the site controller sends aninvitation message on the outbound control channel. The invitationmessage invites members of the first talkgroup to resume registrationrequests.

FIG. 1 is a schematic block diagram illustrating an architecture of atrunked radio system in accordance with some embodiments. The systemincludes a site controller 100 equipped with a transceiver 101 forconducting wireless communications with a plurality of subscriber units.The transceiver 101 may include several antennas for communications ondifferent communications channels, including a duplex control channelthat includes an inbound control channel for communications to the sitecontroller and an outbound control channel for communications to thesubscriber units. The site controller 100 includes a control module 102,which comprises a general- or special-purpose processor 103 and anon-transitory computer-readable memory 104 operatively coupled to theprocessor 103. The memory 103 stores instructions executable by theprocessor and operative to perform the site controller steps describedin further detail below.

In a further embodiment, a subscriber unit apparatus is provided. Thesubscriber unit may comprise a transceiver for communicating on aninbound control channel and an outbound control channel, and a processorcoupled to a non-transitory computer-readable medium storing executableinstructions that, when executed on the processor, are operative to (i)receive a restriction message on the outbound control channel, whereinthe restriction message initiates a restriction period by instructingsubscribers who are not members of the first talkgroup to ceaseregistration requests; (ii) to determine that the subscriber unit is nota member of the first talkgroup; and in response to the determinationthat the subscriber unit is not a member of the first talkgroup, (iii)to determine the end of the restriction period, where the restrictionperiod ends at the earlier of the following times: (a) when apredetermined delay time has passed since the initiation of therestriction period; and (b) when a predetermined silence time has passedsince the receipt of a registration acknowledgement on the outboundcontrol channel; and only after the expiration of the restrictionperiod, to send a registration request from the subscriber unit on theinbound control channel.

The site controller 100 is in wireless communication with a plurality ofsubscriber units, such as subscriber units 110, 111, 112, and 113. Inthe present example, subscriber 110 is a member of talkgroup A,subscriber 111 is a member of talkgroup B, and subscriber 112 is amember of talkgroup C. A subscriber unit may be a member of differenttalkgroups or multiple talkgroups at different times, as illustrated bysubscriber unit 113, which can be a member either or both of talkgroup Aor of talkgroup B.

In the exemplary embodiment of FIG. 1, the site controller 100 iscoupled with a backend network 120 to permit subscriber units registeredwith site controller 100 to communicate over the backend network withother subscriber units being served by other site controllers.

Before they can be served by site controller 100, subscriber units 110,111, 112, and 113 register with site controller 100 by sendingregistration messages to site controller 100 over the inbound controlchannel identifying themselves and the talkgroups of which they aremembers. To complete the registration, site controller 100 sendsregistration grants to the respective subscriber units over the outboundcontrol channel.

Under some conditions, a large number of subscriber units may attempt tosend registration messages to site controller 100 at substantially asame time. This leads to multiple collisions between messages on theinbound control channel. Many of these messages are likely to beunintelligible to the site controller 100. Site controller 100 will beunable to register the subscriber units whose messages were not receivedor were unintelligible, and in turn, site controller 100 will be unableto send registration grants to the requesting subscriber units.Consequently, the subscriber units will attempt to re-send theirregistration requests, which will further increase the traffic on theinbound control channel. This situation is referred to herein as a massregistration condition.

A mass registration condition may arise from several possible scenarios.For example, if a site is temporarily out of service, a massregistration condition may arise when the site comes back online. A massregistration condition may arise when a large number of subscriber unitsare turned on at substantially the same time, or they all arrive in thevicinity of a site controller at substantially the same time. Suchsituations may arise when, for example, workers equipped with subscriberunits begin their shift at the same time, or when rescue or lawenforcement personnel arrive at a particular location at substantiallythe same time. A mass registration condition may arise when one sitecontroller fails, and the subscriber units that were formerly registeredwith the failed site controller begin sending registration requests tonearby site controllers.

FIG. 2 is a schematic message flow diagram illustrating exemplarycommunications between a site controller 200 and subscriber units thatare members of three talkgroups during a mass registration condition.Subscriber units that are members of talkgroup A are represented byentity 210, subscriber units that are members of talkgroup B arerepresented by entity 211, and subscriber units that are members oftalkgroup C are represented by entity 212. Extrapolation of theprinciples described in FIG. 2 to situations involving any number oftalkgroups will be apparent to one of ordinary skill in the art.

In FIG. 2, horizontal arrows are representative of messages exchangedbetween the site controller 200 and the subscriber units. Leftwardarrows represent one or more messages sent on the inbound controlchannel to the site controller 200. Rightward arrows represent one ormore messages sent on the outbound control channel by the sitecontroller 200. Messages sent by the controller 200 may typically bereceived by members of multiple talkgroups, even if they pertain only toa single talkgroup, but for efficiency of illustration, the arrows areshown to terminate at the talkgroup to which the outbound message isintended to pertain. It should also be noted that, for efficiency ofconveying the concepts described herein, not every message exchangedbetween subscriber units and site controller is illustrated. Moreover, asingle horizontal line may represent more than one message.

In step 220, during a mass registration condition, the site controller200 receives at least one registration request from members 210 oftalkgroup A. It should be noted that the received registration requestor requests may be one of many attempted requests sent by members oftalkgroups A, B, and C. However, many of the attempted registrationrequests may not be received by site controller 200 due to the massregistration condition.

In response to the registration request received from a member oftalkgroup A, the site controller 200 sends a restriction message 222 onthe outbound control channel. The restriction message instructs themembers 210 of talkgroup A to hold off temporarily on the sending ofregistration requests. By postponing registration requests from membersof a particular talkgroup (in this example, talkgroup A), the sitecontroller 200 operates to alleviate the immediate demands on theinbound control channel.

The restriction message 222 may be a separate dedicated message, thesole purpose of which is to convey the restriction period. In otherembodiments, and to make the most efficient use of the control channel,the restriction message 222 may itself be a registration grant for amember of talkgroup A. For example, the restriction message may be aregistration grant that makes use of a specialized opcode, or it mayinclude particular flags or other information in the message payloadthat indicates that the registration grant is also a restrictionmessage. Such information in a registration grant that identifies theregistration grant as a restriction message is referred to herein as arestriction code. Moreover, the restriction message 222 may indicate tothe subscriber units that the associated talkgroup is registered withthe site controller 200. A restriction message may be sent several timesto ensure receipt by members of a restricted talkgroup.

The restriction message 222 is sent at the beginning of a firstrestriction period 224, during which members 210 of talkgroup A hold offon sending registration requests. Members 211 and 212 of othertalkgroups are not restricted from sending registration requests byrestriction message 222. As a result, those subscriber units maycontinue to attempt to send registration requests. For example, in step226, one or more members of talkgroup B send registration requests tothe site controller 200. If the imposition of the first restrictionperiod 224 has been sufficient to alleviate the mass registrationcondition, then the site controller 200 may respond to the talkgroup Brequests with ordinary registration grants. However, in the exampleillustrated in FIG. 2, the mass registration condition persists despitethe imposition of the first restriction period.

Since the mass registration condition persists when the requests 226 aresent, the site controller 200 initiates a second restriction period 228by sending a restriction message 230 that instructs members 211 oftalkgroup B to hold off temporarily on the sending of registrationrequests. The imposition of the second restriction period 228 furtheralleviates the demands on the inbound control channel. As illustrated inFIG. 2, the first restriction period 224 can overlap with the secondrestriction period 228, although this is not necessarily always thecase.

In this example, the imposition of both the first and second restrictionperiods is sufficient to eliminate the mass registration condition.Consequently, registration requests 232 sent by members 212 of talkgroupC do not lead to the imposition of a third restriction period. Instead,site controller 200 responds to the registration requests 232 byregistering the members 212 of talkgroup C and responding to theregistration requests 232 with registration grants 234. It should beunderstood that, in other situations, the site controller 200 may imposea third restriction period, and so on with additional talkgroups, untilsufficient restrictions have been imposed to alleviate the massregistration condition.

As illustrated at step 236, the site controller 200 sends an invitationmessage at the end of the first restriction period 224. The invitationmessage 236 indicates to members 210 of talkgroup A that they may resumetheir individual registration requests.

The time at which a restriction period ends may be different indifferent embodiments. In some embodiments, the restriction period endswhen a predetermined delay time has passed since the initiation of therestriction period. For example, the restriction period may last for apredetermined delay time of 5-10 seconds. The use of a predetermineddelay time imposes a reasonable upper bound on the length of arestriction period. As an alternative to a predetermined delay time, therestriction message can include information identifying the length ofthe delay time to be used for the relevant restriction period. If, in aparticular instance, the mass registration persists even after the delaytime has expired and an invitation message has been sent, the sitecontroller 200 can initiate a new restriction period.

In some embodiments, the site controller 200 may determine the end ofthe restriction period (and consequently the timing of the invitationmessage) by monitoring the traffic on the inbound control channel. Forinstance, the site controller 200 may end the restriction period when apredetermined silence time has passed during which the site controller200 has not received any registration message on the inbound controlchannel. For example, the site controller 200 may end the restrictionperiod when a silence time of 2-5 seconds has passed without receipt ofany inbound registration message. The use of a silence time helps toensure that the restriction period does not last substantially longerthan necessary to register those members of talkgroups that have notbeen restricted, but last sufficiently long to at least temporarilyalleviate the condition. As a result, it is not necessary for the sitecontroller 200 to calculate in advance an estimate of the amount of timethat will be required for registration of unrestricted talkgroups to becompleted.

In some embodiments, the site controller 200 makes use of both a delaytime and a silence time. For example, the site controller may end therestriction period at the earlier of the following times: (a) when thedelay time has passed since the initiation of the restriction period;and (b) when the silence time has passed since the receipt of aregistration request. This places an upper bound on the length of arestriction period while allowing that the restriction period can beshortened if the inbound control channel is at least momentarily clearof registration request traffic. In such an embodiment, the duration ofthe silence time is selected to be shorter than the duration of thedelay time.

During the restriction period, a substantial majority of registrationrequests received by the site controller 200 are likely to be requestsfrom members of talkgroups that have not been subjected to a restrictionmessage. However it is still possible to receive a registration requestfrom a member of a talkgroup that is subject to a restriction period. Inparticular, some subscriber units may have been turned off or out ofrange, or served by a different site controller when the restrictionmessage was sent. In some embodiments, registration requests sent bymembers of restricted talkgroups are processed as if the restrictionwere not in place, as such requests were likely to have been innocentlysent. In other embodiments, the restriction message 222 may be re-sent.

After the site controller 200 sends an invitation 236 to the members 210of talkgroup A, those subscriber units may submit registration requests238. In some embodiments, the members 210 of talkgroup A avoid collisionbetween their registration requests by introducing a random delay in thetiming of their respective registration requests. The site controller200 responds to the registration requests 238 by registering the members210 of talkgroup A and responding to the registration requests 238 withregistration grants 240.

When the second restriction period 228 ends, the site controller 200sends an invitation message 242 inviting the members 211 of talkgroup Bto submit registration requests Immediately or after a random delay, themembers 211 of talkgroup B submit their registration requests 244. Thesite controller 200 responds to the registration requests 244 byregistering the members 211 of talkgroup B and responding to theregistration requests 244 with registration grants 246.

FIG. 3 is a flow chart illustrating the operation of a site controllerin accordance with some embodiments. In step 302, the site controllerreceives a registration request from a subscriber unit that is a memberof talkgroup A.

In step 304, the site controller determines whether the inbound controlchannel is in a mass registration condition. This determination may bemade using one or more of various different techniques in differentembodiments. For example, the determination that the inbound controlchannel is in a mass registration condition may be made by determiningwhether the rate of incoming registration request messages exceeds apredetermined threshold rate. In some embodiments, the determination maybe made by predicting that a large amount of registration requests willbe made at particular times, such as at the beginning of a work shift,or when a site controller has come back online after a period of beingoffline, or when service has been lost at a neighboring site controller.Other possibilities exist as well.

If there is no mass registration condition, then in step 306, the sitecontroller responds to the registration request by registering thesubscriber unit and responding to the registration request with aregistration grant. If there is a mass registration condition, then instep 308, the site controller determines whether talkgroup A iscurrently subject to a restriction period. If talkgroup A is not yetsubject to a restriction period, then in step 310, the site controllersends a restriction message to the members of talkgroup A, therebyinitiating a restriction period for talkgroup A.

The site controller is then responsible for identifying the end of therestriction period. In step 312, the site controller determines whetherthe predetermined delay time has expired since the restriction messagewas sent in step 310, and in step 314, the site controller determineswhether a predetermined silence time has expired since a registrationrequest was last received by the site controller. If either of thoseconditions has occurred, the site controller progresses toward thesending of an invitation message. In some embodiments, as illustrated instep 316, if there is a call in progress, the site controller may waituntil the end of the call before sending an invitation message. In step318, the site controller sends an invitation message to the members oftalkgroup A. In some embodiments, step 316 is not performed, and thesite controller does not wait until the end of the call before sendingan invitation message. In such embodiments, members of talkgroup A canregister and, if the call is in progress and if it relates to talkgroupA, those newly-registered members can join the call in progress.

Returning to step 308, if a member of talkgroup A sends a registrationrequest despite the restriction period already being imposed ontalkgroup A, it is likely that the subscriber unit did not receive therestriction message. In some embodiments, the site controller may thenprocess the registration request and send a registration grant despitethe imposition of the restriction period (see step 306). In otherembodiments, the site controller may re-send the restriction message ina manner similar to that set forth in step 310.

In the embodiments described above the restriction messages singled outparticular talkgroups whose members were requested not to sendregistration requests. In other embodiments, described below,restriction messages request that all subscriber units except for aselected talkgroup refrain from sending registration requests.

According to an embodiment described herein, a site controller detectsthat an inbound control channel is in a mass registration condition.During the mass registration condition, the site controller receives aplurality of registration requests from subscribers over the inboundcontrol channel. The registration requests include requests fromsubscribers associated with a plurality of different talkgroups. Thesite controller selects a first talkgroup from among the first pluralityof talkgroups. The site controller then initiates a first restrictionperiod by sending a first restriction message on an outbound controlchannel, wherein the first restriction message instructs subscribers whoare not members of the first talkgroup to cease registration requests.During the first restriction period, the site controller registersmembers of the first talkgroup. During the first restriction period, asubstantial majority of talkgroup members registered by the sitecontroller may be members of the first talkgroup.

The first restriction message is received at a subscriber unit. If thesubscriber unit determines that it is not a member of the firsttalkgroup, it determines the expiration of the restriction period byidentifying one of, or the earlier of, the following times: (a) when apredetermined delay time has passed since the initiation of the firstrestriction period; and (b) when a predetermined silence time has passedsince the receipt of a registration acknowledgement on the outboundcontrol channel. Only after the restriction period has expired, andassuming no further restriction period is established in the interim,the subscriber unit sends a registration request to the site controlleron the inbound control channel.

FIG. 4 is a schematic message flow diagram illustrating exemplarycommunications between a site controller 400 and talkgroup membersduring a mass registration condition in some embodiments. The schema ofFIG. 4 should be interpreted as described above with respect to FIG. 2.

The site controller 400 receives registration requests 402, 404, and 406from one or more members 410 of talkgroup A, members 411 of talkgroup B,and members 412 of talkgroup C, respectively. The site controller 400then selects one of the talkgroups from which it received a registrationrequest. In this example, the site controller selects talkgroup A. Instep 408, the site controller 400 initiates a first restriction period414 by sending a restriction message 408 on the outbound controlchannel. The restriction message 408 requests that registration duringthe first restriction period be restricted to members 410 of talkgroupA.

The restriction message 408 may itself be a registration grant for oneor more subscriber units that are members of talkgroup A. For example,the restriction message may be a registration grant that makes use of aspecialized opcode, or it may include particular flags or otherinformation in the message payload that indicates that the registrationgrant is also a restriction message for subscriber units that are notmembers of talkgroup A. Such information in a registration grant thatidentifies the registration grant as a restriction message is referredto herein as a restriction code. The restriction message 408 furtherincludes information identifying the selected talkgroup (in thisexample, talkgroup A) that is permitted to individually register itsmembers during the restriction period. Moreover, the restriction message408 may indicate to the subscriber units that the associated talkgroupis registered with the site controller 400. A restriction message may besent several times to ensure receipt by members of the restrictedtalkgroups and/or the selected talkgroup A.

During the first restriction period 414, members 410 of the selectedtalkgroup, talkgroup A, continue to submit individual registrationrequests 416 to the site controller 400. The site controller 400registers the requesting members 410 of talkgroup A and confirms theregistration by sending registration grants 418 to the respectivesubscriber units.

In some embodiments, each of the the restricted subscriber units isresponsible for determining the end of a restriction period. The time atwhich a restriction period ends may be different in differentembodiments. In some embodiments, the restriction period ends when apredetermined delay time has passed since the initiation of therestriction period. For example, the restriction period may last for apredetermined delay time of 5-10 seconds. The use of a predetermineddelay time imposes a reasonable upper bound on the length of arestriction period. If, in a particular instance, the mass registrationpersists even after the delay time has expired and an invitation messagehas been sent, the site controller 200 can initiate a new restrictionperiod. As an alternative to a predetermined delay time, the restrictionmessage can include information identifying the length of the delay timeto be used for the relevant restriction period.

In some embodiments, the subscriber units may determine the end of therestriction period (and consequently the time at which they arepermitted to send registration requests) by monitoring the traffic onthe outbound control channel. For instance, a subscriber unit maydetermine that the restriction period has ended when a predeterminedsilence time has passed during which the subscriber unit has notdetected any registration grant sent on the outbound control channel.For example, a subscriber unit may determine that the restriction periodhas ended when a silence time of 2-5 seconds has passed without thedetection of any outbound registration grant. The use of a silence timehelps to ensure that the restriction period does not last substantiallylonger than necessary to register the members of the selected talkgroup.As a result, it is not necessary for the site controller 400 or for thesubscriber units to calculate in advance an estimate of the amount oftime that will be required for registration of members of the selectedtalkgroup to be completed. Subscriber units that have already registeredwith the site controller 400 need not dedicate any resources todetermining an end to the restriction period.

In some embodiments, the subscriber units make use of both a delay timeand a silence time. For example, a subscriber unit may determine thatthe restriction period has ended at the earlier of the following times:(a) when the delay time has passed since the initiation of therestriction period; and (b) when the silence time has passed since thereceipt of a registration grant. This places an upper bound on thelength of a restriction period while allowing that the restrictionperiod can be shortened if the outbound control channel is at leastmomentarily clear of registration grant traffic. In such an embodiment,the duration of the silence time is selected to be shorter than theduration of the delay time.

Once members 411 of talkgroup B and members 412 of talkgroup C determinethat the first restriction period 414 has ended, they begin to sendregistration requests 420 and 422, respectively. In some embodiments,the subscriber units of talkgroup B 411 and talkgroup C 412 avoidcollision between their registration requests by introducing a randomdelay in the timing of their respective registration requests.

In some situations, the imposition of the first restriction period 414may be sufficient to alleviate the mass registration condition, in whichcase further restriction periods may not be necessary. However, in theexample illustrated in FIG. 4, the inbound control channel is still in amass registration condition despite the first restriction period 414. Asa result, the site controller 400 makes a new selection of a talkgroupfrom among the registration requests 420 and 422 that it has received.In this example, the site controller 400 selects talkgroup B. The sitecontroller 400 then initiates a second restriction period 424 by sendinga restriction message 426 on the outbound control channel, identifyingtalkgroup B as the selected talkgroup and restricting the remainingtalkgroups (talkgroup C).

In some embodiments, the second restriction period 424 does not apply tomembers 410 of talkgroup A. This way, if the first restriction period414 was not sufficiently long to permit registration of all members 410of talkgroup A, those members can continue to submit registrationrequests during the second restriction period 424.

During the first restriction period 414 and second restriction period424, a substantial majority of registration requests received by thesite controller 400 are likely to be requests from members of talkgroupsA and B, which are the talkgroups that have been selected forregistration during the restriction periods. However it is stillpossible for the site controller 400 to receive a registration requestfrom a member of another talkgroup during the restriction periods 414and 424, such as a member of talkgroup C 412. In particular, somesubscriber units that are members of talkgroup C 412 or other talkgroupsthat have not yet been selected may have been turned off, out of range,or served by a different site controller when the restriction messages408 and/or 426 were sent. In some embodiments, registration requestssent by members of such unselected talkgroups are processed as if therestriction were not in place, as such requests were likely to have beeninnocently sent. In other embodiments, the site controller may re-sendthe restriction message.

During the second restriction period 424, members 411 of the selectedtalkgroup, talkgroup B, continue to submit registration requests 428 tothe site controller 400. The site controller 400 registers therequesting members 411 of talkgroup B and confirms the registration bysending registration grants 430 to the respective subscriber units.

The members 412 of the restricted talkgroup C then make a determinationof when the second restriction period 424 has ended. After the end ofthe second restriction period 424, subscriber units 412 begin to sendregistration requests 432. In some embodiments, the subscriber units 412avoid collision between their registration requests 432 by introducing arandom delay in the timing of their respective registration requests432. The use of such random delays is well understood by those skilledin the art. The site controller 400 registers the requesting members 412of talkgroup C and confirms the registration by sending registrationgrants 434 to the respective subscriber units.

FIG. 5 is a flowchart illustrating the operation of a site controller insome embodiments. In step 500, the site controller receives a pluralityof registration requests from subscriber units. The registrationrequests correspond to at least two different talkgroups.

In step 502, the site controller determines whether it is in a massregistration condition. This determination may be made using one or moreof various different techniques in different embodiments, as set forthabove.

If there is no mass registration condition, then in step 504, the sitecontroller responds to the registration request by registering thesubscriber units and responding to the registration requests withregistration grants that do not include a restriction code. If theinbound control channel is in a mass registration condition, then instep 506, the site controller selects a particular talkgroup from amongthe talkgroups associated with registration requests received in step500.

The selection of a particular talkgroup may be conducted in variousways. For example, the selection may be random, it may depend on theorder in which registration requests are received, it may depend on therelative number of registration requests being received from differenttalkgroups, it may depend on some predetermined priority betweentalkgroups, or it may depend on some combination of these factors. Otherpossibilities exist as well.

Having selected a particular talkgroup, the site controller in step 508sends a restriction message that temporarily restricts registration tomembers of the selected talkgroup. As set forth above, the restrictionmessage may be a registration grant message that includes a restrictioncode that identifies the registration grant as a restriction message, ormay be a dedicated restriction message. The restriction message alsoincludes information identifying the selected talkgroup. More than onerestriction message may be sent out at step 508.

FIG. 6 is a flowchart illustrating the operation of a subscriber unit insome embodiments, such as the embodiments depicted in FIGS. 4 and 5. Instep 600, the subscriber unit receives a restriction message on theoutbound control channel, which in some embodiments, may also be aregistration grant. The restriction message may not be addressed to thatparticular subscriber unit. Nevertheless, the subscriber unit processesthe restriction message by determining in step 602 whether a restrictioncode is present in the restriction message. If no restriction code ispresent, the subscriber unit may then send its own registration requeston the inbound control channel in step 604 according to knowncollision-avoidance techniques.

If the restriction message does include a restriction code, thesubscriber unit continues to process the restriction message bydetermining in step 606 whether it is a member of the selected talkgroupidentified in the restriction message. If the subscriber unit is amember of the selected talkgroup, the subscriber unit may then proceedwith sending its own registration request in step 604.

If, on the other hand, the subscriber unit is not a member of theselected talkgroup identified in the restriction message, then thesubscriber unit recognizes that it is subject to a restriction period,and waits until the expiration of the restriction period before sendingits own registration request. To determine whether the restrictionperiod has expired, the subscriber unit determines in step 608 whether apredetermined delay time has expired. If so, the restriction period isconsidered to have ended, and the subscriber unit can send its ownregistration request in step 604, perhaps using a collision-avoidancetechnique.

If the delay time has not expired, the subscriber unit determines instep 610 whether a predetermined silence time has passed since aregistration grant was last received over the outbound control channel.If so, the restriction period is considered to have ended, and thesubscriber unit can send its own registration request in step 604,perhaps using a collision-avoidance technique.

In the foregoing specification, specific embodiments have beendescribed. However, one of ordinary skill in the art appreciates thatvarious modifications and changes can be made without departing from thescope of the invention as set forth in the claims below. Accordingly,the specification and figures are to be regarded in an illustrativerather than a restrictive sense, and all such modifications are intendedto be included within the scope of present teachings.

The benefits, advantages, solutions to problems, and any element(s) thatmay cause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeatures or elements of any or all the claims. The invention is definedsolely by the appended claims including any amendments made during thependency of this application and all equivalents of those claims asissued.

Moreover in this document, relational terms such as first and second,top and bottom, and the like may be used solely to distinguish oneentity or action from another entity or action without necessarilyrequiring or implying any actual such relationship or order between suchentities or actions. The terms “comprises,” “comprising,” “has”,“having,” “includes”, “including,” “contains”, “containing” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises, has,includes, contains a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus. An element proceeded by“comprises . . . a”, “has . . . a”, “includes . . . a”, “contains . . .a” does not, without more constraints, preclude the existence ofadditional identical elements in the process, method, article, orapparatus that comprises, has, includes, contains the element. The terms“a” and “an” are defined as one or more unless explicitly statedotherwise herein. The terms “substantially”, “essentially”,“approximately”, “about” or any other version thereof, are defined asbeing close to as understood by one of ordinary skill in the art, and inone non-limiting embodiment the term is defined to be within 10%, inanother embodiment within 5%, in another embodiment within 1% and inanother embodiment within 0.5%. The term “coupled” as used herein isdefined as connected, although not necessarily directly and notnecessarily mechanically. A device or structure that is “configured” ina certain way is configured in at least that way, but may also beconfigured in ways that are not listed.

It will be appreciated that some embodiments may be comprised of one ormore generic or specialized processors (or “processing devices”) such asmicroprocessors, digital signal processors, customized processors andfield programmable gate arrays (FPGAs) and unique stored programinstructions (including both software and firmware) that control the oneor more processors to implement, in conjunction with certainnon-processor circuits, some, most, or all of the functions of themethod and/or apparatus described herein. Alternatively, some or allfunctions could be implemented by a state machine that has no storedprogram instructions, or in one or more application specific integratedcircuits (ASICs), in which each function or some combinations of certainof the functions are implemented as custom logic. Of course, acombination of the two approaches could be used.

Moreover, an embodiment can be implemented as a computer-readablestorage medium having computer readable code stored thereon forprogramming a computer (e.g., comprising a processor) to perform amethod as described and claimed herein. Examples of suchcomputer-readable storage mediums include, but are not limited to, ahard disk, a CD-ROM, an optical storage device, a magnetic storagedevice, a ROM (Read Only Memory), a PROM (Programmable Read OnlyMemory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM(Electrically Erasable Programmable Read Only Memory) and a Flashmemory. Further, it is expected that one of ordinary skill,notwithstanding possibly significant effort and many design choicesmotivated by, for example, available time, current technology, andeconomic considerations, when guided by the concepts and principlesdisclosed herein will be readily capable of generating such softwareinstructions and programs and ICs with minimal experimentation.

The Abstract of the Disclosure is provided to allow the reader toquickly ascertain the nature of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims. In addition, in theforegoing Detailed Description, it can be seen that various features aregrouped together in various embodiments for the purpose of streamliningthe disclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments require morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter lies in less than allfeatures of a single disclosed embodiment. Thus the following claims arehereby incorporated into the Detailed Description, with each claimstanding on its own as a separately claimed subject matter.

We claim:
 1. A method comprising: detecting that an inbound controlchannel is in a mass registration condition; during the massregistration condition, receiving a first plurality of registrationrequests from subscribers over the inbound control channel, wherein theregistration requests are associated with a first plurality oftalkgroups; selecting a first talkgroup from among the first pluralityof talkgroups; initiating a first restriction period by sending a firstrestriction message on an outbound control channel, wherein the firstrestriction message instructs subscribers who are not members of thefirst talkgroup to cease registration requests; and registering membersof the first talkgroup during the first restriction period, wherein asubstantial majority of talkgroup members registered during the firstrestriction period are members of the first talkgroup.
 2. The method ofclaim 1, wherein the first restriction message is a registration grant,and wherein the registration grant includes a restriction code thatidentifies the registration grant as a restriction message.
 3. Themethod of claim 1, further comprising: after the first restrictionperiod, receiving a second plurality of registration requests fromsubscribers over the inbound control channel, wherein the registrationrequests are associated with a second plurality of talkgroups; selectinga second talkgroup from among the second plurality of talkgroups; and inresponse to a determination that the inbound control channel is still ina mass registration condition, initiating a second restriction period bysending a second restriction message on the outbound control channel,wherein the second restriction message instructs subscribers who are notmembers of the first talkgroup or the second talkgroup to ceaseregistration requests.
 4. The method of claim 1, further comprising:receiving the first restriction message at a subscriber unit;determining, at the subscriber unit, that the subscriber unit is not amember of the first talkgroup; in response to the determination that thesubscriber unit is not a member of the first talkgroup, determining theend of the first restriction period, where the restriction period endsat the earlier of the following times: (a) when a predetermined delaytime has passed since the initiation of the restriction period; and (b)when a predetermined silence time has passed since the receipt of aregistration acknowledgement on the outbound control channel; and onlyafter the expiration of the first restriction period, sending aregistration request from the subscriber unit on the inbound controlchannel.